On Fri, 2005-01-21 at 06:43 -0800, michael wrote: > setattr (self, key, property (fget, fset, fdel))
> it gives me > > <property object at 0x4028102c> > > What am I doing wrong here Properties must be defined in the class, not the instance, to work as expected. (Edit: Nick Coghlan explained this more accurately). You can dynamically generate properties in a metaclass or class factory, and you can add them to a class after the class is created (even from an instance of that class). If you add properties to an instance of a class rather than the class its self, though, you won't get the expected results. .class Fred(object): . def __init__(self): . self._name = 'fred' . def getname(self): . return self._name . def setname(self, newname): . self._name = newname . name = property(getname, setname) . .f = Fred() .print f.name . .# Works: .class Fred2(object): . def __init__(self): . self._name = 'fred2' . def getname(self): . return self._name . def setname(self, newname): . self._name = newname . .Fred2.name = property(Fred2.getname, Fred2.setname) .f2 = Fred2() .print f2.name . .# Won't work: .class Fred3(object): . def __init__(self): . self._name = 'fred3' . def getname(self): . return self._name . def setname(self, newname): . self._name = newname . .f3 = Fred3() .f3.name = property(f3.getname, f3.setname) .print f3.name . .# Also won't work .f3 = Fred3() .f3.name = property(Fred3.getname, Fred3.setname) .print f3.name . .# This will work, though, because while it adds the property .# after the instance is created, it adds it to the class not .# the instance. .f3 = Fred3() .Fred3.name = property(Fred3.getname, Fred3.setname) .print f3.name The chances are that whatever you want to do with dynamically created properties is better done with __getattr__ and __setattr__ instead. If they don't fit the bill, you can add properties to the class from its instances. I intensely dislike this though, personally. I'd want to look into using a class factory or metaclass to do the job if __getattr__ and __setattr__ are insufficient or unacceptable. -- Craig Ringer -- http://mail.python.org/mailman/listinfo/python-list
